Pb-acid batteries, among others, are known to be susceptible to electrolyte concentration variations from top to bottom. This problem is particularly acute during the recharge of deep discharge batteries. In this regard, the heavy H.sub.2 SO.sub.4 formed at the plates during recharge settles to the bottom of the battery causing high concentrations of H.sub.2 SO.sub.4 thereat and weaker concentrations at the top. The electrolyte concentration imbalance is known as electrolyte stratification and is detrimental to battery performance and life.
Mixing or circulation of the electrolyte within the battery to promote concentration uniformity is known and a variety of arrangements have heretofore been proposed to effect this circulation. Sundberg U.S. Pat. No. 3,083,253, for example, describes air-lift-type pumps wherein the lift gas may be provided either by means of an external pump or by the in situ electrolysis of the electrolyte. External air pumps however are not only cumbersome, but require ancillary plumbing and battery vent system capable of exhausting the extra air from the battery. Generating the pumping gas by electrolytic dissociation of the electrolyte produces very small bubbles which are effective pumpers only if contained within small diameter lift tubes which requires a multiplicity of such tubes distributed throughout the cell element (i.e., alternately interspersed positive and negative polarity plates) in order to move enough electrolyte to be practical. Sundberg U.S. Pat. No. 3,305,404, inter alia, on the other hand, bubbles air beneath the cell element and allows the bubbles to rise between the several plates thereof. Such arrangements however have much of the complexity of the air-lift-type pumps and tend to promote oxidation of the plates. Halsey U.S. Pat. No. 734,549 and Scholl et al U.S. Pat. No. 4,194,060 employ externally driven impellers in the cell compartment. Needless to say, such arrangements are not only complex and expensive to manufacture but are also subject to leakage at the seals and wear at the impeller bearings.
Von Brimer U.S. Pat. No. 3,597,278, utilizes a magnetic field to effect circulation. Von Brimer positions the cell element, or portions thereof, between opposite polarity magnets so that the electrolyte is magnetically circulated when current flows between the element's plates. In one embodiment, Von Brimer locates a plurality of magnets between the several plates through openings in the interplate separators. This embodiment adds considerable weight to the battery, increases the risk of shortened life due to internal shorting through the openings in the separator and results in reduced performance due to the wide spacing between the plates/electrodes of the cell element. Alternatively, Von Brimer proposes that the magnetic field be established between the plates by magnets placed outside the cell element. This embodiment would require that the magents be widely spaced apart which would require very strong and hence very heavy and/or expensive magnets.
It is an object of the present invention to provide an electric storage battery with an uncomplicated, inexpensive, electrolyte-mobilizing magnetohydrodynamic pump adjacent the cell element for circulating electrolyte within the battery. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.